This invention relates generally to forming of fiber composites, for example as are used in high-efficiency air filtration; and more particularly, the invention concerns provision of a filter composite comprising multiple layers of porous material, of such characteristics as enable the composite to be self-supporting, i.e., without need for wire backing or other auxiliary support adjacent areal extents of the composite. Such wireless composites are of great advantage, as respects ease of manufacture, use in filtering, and ease of disposal. Wire-supported filters require wire trimming, producing sharp edges which can and do injure hands of workers manufacturing filters.
There is need for longer-life filters capable of efficiently filtering particulate from gas streams, and there is need for efficient, effective methods of producing such filters. There is also need for preventing escape of smaller diameter glass fibers from filter structures. The disclosure of U.S. Pat. No. 3,690,852, incorporated herein by reference, concerns production of a filter comprising two layers of fibers of different sizes. The present invention improves upon the methods described in that patent, as will be seen.
The present invention also improves upon apparatus disclosed in that patent in that it provides for a self-supporting, multi-layer composite requiring no wire backing, as referred to above.